Finder for photographic cameras



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July 24, 1928.

L. E. w. VAN ALBADA FINDER FOR PHOTOGRAPHIC cmsms,

Filed Aug. 24, 1923 Patented July 24, 1928.

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for photographiccameras which, inprincip1e,'-corresponds' to the collimator well-known as .a sighting means for fire-arms. ,Besules, by Iusing,' as has been suggested forfinders, as a collective member of the collimator a semi-lens, such'a finderadmits in .t-he'direction, perpendicular to. the surface oflintersection of the se1ni-lens,;o-f only estimating the size of the-image because in the one half of the field of view one only sees the marks and inthe other;half only the object to be taken.-'-This; drawback can be removed by using asacollective member such a. member which has the re-fractivepower zero at least overa zone approximately concentrie with its axis. In that case the collimator. disc/ is supposed to be so'i'eonstructed as'to substantially admit of the free View upon therespective object. lVhen fusing such afinder it must be brought at such a distance from the eye that the rays emerging directlyfrom thev object to be taken enter the eye through thatpart or those parts having the refractive power zero, whilst through the remaining part of the collective membervthe lines or the marks of thecollimator aresimultaneously visible. FA suitable collective member is, for instance, obtained by piercingan ordinary lens in the centre in the axial direct-ion or by grinding on both its sides asmall, plane surface perpendicular to the lens a'xish, pnAnother suitable collective member is attained by using alens which has no continuous spherical surfaces but in which the spherical surfaces are interrupted by zones having the refractive power zero, such as plane parallel .zones.;.-:lt. is vpos ible to m-ake such astep-like lens for instance in such a Way that a numberof thin, round, plane-parallel 5 glass plates, whose diameters are graduated aceordingto' the lens-curvature to be made. are cemented centrically with each other and, on grinding the spherical surfaces, the margins'of the single lamellae are only ground off to such an extent that between two consecutive la-mellze a plane-parallel ring each is allowed to remain. In a collimator lens of this kind the observing eye then also sees through the plane-parallel parts of the lens the object to be taken and, simultaneously through the collective parts of the lens the lines or the marks of the collimator.

Another constructional form is attained rrnDER' FOR PHOTOGRAPHIC CAMERAS. 5

Application filed August 24, 1923, Serial No.

'wmm van amateur 'AMs'rERDAM;nETHEItLAnns, lemma 'ro'rnn F nn cARnznIss, or JENA, GERMANY.

659,170, and in Germany ,Septeniber 6, 1922.-

feet by means ofa concave mirror. i In that case the latter mirrorniust naturally, on the one hand, not prevent the rays coming from theobject to be taken'from entering the eye, it musttherefore in additionto its capacity as a concave mirrorbe transparent andhave the refractive power zero for the' traversing rays, and on the other'hand' the collimator disc, which with "this arrangement getsin front of the eye, must have in its centre a corresponding sight-opening for the passage .of the rays A transparent concave mirror may be embodied in different ways. An ob vious constructional form consists in providing a. correspondingly meniscal glassplate, having the refractive power zero for the traversing rays, on one side. with a semiby bringing about the efcave mirror is simultaneously transparent and reflecting over itswhole, surface. It may also sufiice to use as a concave mirror an uncoated, meniscal glass plate. l lVith a view to adapting in this case the luminosity of the object to be taken. and viewed through the glass plate to the considerably less bright image of the collimator, the meniscal glass plate is suitably made .of smoked or some other coloured glass. .It is also possible to replace the physical fraydivision, which fis effected invthe aforesaid manner, by a godmetrical ray division by silvering a meniscal glass plate, e.. g. [in stripes or gratings in such a Way that transparent andrefiecting elements interchange with each other over the entire reflecting surface. I j I Another suitable constructional form is attained by disposing thecollimator withits axis approximately perpendicular to the objective axis of the photographic camera and by locating in frontof this collimator a plane-parallel glass plate inclined to the obect1ve axis at about 459, which glass plate on the one hand reflects the rays emerging from the collimator into the eye of the ob server and vwhich on the other hand simul taneously admits of looking towards the object to be taken. By carrying out with this arrangement the marks as gaps of the other: wise opaque collimator disc, thesame can be illuminated from above in a very favourable way. Also in this case it will be. advisable, in order to compensate the difference in luminosity between the object viewed through the plane-parallel plate and the image of the Ion numbcli of different constructional examples of finders whereby the photographicjcamera, with which the find eris a ss uine d to be rigidly connected, shown by the upper part of the outline. Fig. l -shows in: a ".longitud'inal section I a finder with planely ground lens, Fig. 2 shows aiside elevation ot the same 'finder; Fig. 3 shows in-a side' 'elevation' another lens form for the same finder; Fig.4 shows the same lensin a front'view ;*Fig. 5illnstratesa 'finder with a concave mirror in a longitudi- 'nal section; Fig. 6-is a c'ros'ssec'tion on the line 6-6 ofFig. 5; FigJ'Z-i's-a vertical sec tion-ofafinder with 'a collimator disposed perpendicularly to the objective axis anda plane-parallel plate fitted I in "front of the gm I; a clin y g; .111. :With the first Y "constructional "eriample shown in Figs. 1 and 2 a base plated fixed on; the camera carries on I the one hand a collimator lens b"an'd= on' 'the other hand wire frame 0 embodying-the collimator disc. which represents a continuous "series of marks anddelimits the image field, the'lateral edges-ct which fra'me being carved in the opposite directiongi'n orrlerto compe'n sate the distortion'caus ed by the-lens The latterfhas'bn its convex: side in the'centre a small plane surface b ,thus acting the range otthis surface 6 as a plane-parallel plate. Hence the observer views through this'planerparallel part or the lens 6 the obthe. protection of thesilverveoatingthere is disposed directly in front of the plate f a second, meniscal glass plate b. On the colli- -mator disc gnlade of.sheetmetal thesurface "corresponding,totlieilimage field is painted black, whilst 'all" around projects a white is only; diagrammatically,- ,margin 1 K11 observer looking through the sight-opening 9 secs therefore through the .cconcave mirror faiths ObjGCFLiOghQ lIlkGD. in such a Way, that the image field is delimited all around by alight margin cOne then.already gets in th'e finder approximately the same 'impression as producedwvith the usual execution by'the finished photograph and avill'th'n's'he able 'to'judge'quite wcllithe final ell ect of the'image before the exposure. *"Thejfi'nder illustrated-in Fi 7 has aicollimator of the usual form, i. e.- a plano1con ve. lens 2' anda collimator disc is which are rigidly connected by a casing l,.the axis of which collimator is disposed perpendicularly to the objectiveaxis. The collimator disc is is a glass plate, on whichltheimarks are formed by gaps of an opaqu'e coating, so that the same always appearito be. Well illuminated by the light 'diifuselynentering from outside. In front ofthe lens 71 is disposed -a plane-parallel glass plate 112,! inclined to the objective axis at 45 and carry.-

ing 1 on its lower-side a I grate-like mirror coating, wherebyit reilect's the mark image intothe eye ofthe observen whilst simultaneously the object to be taken is visible through the plate mQ In order toprotect the 'mirror coating a second plane-parallel plate n'is cemented to the plate 172.. A mount jeet to be taken in full size, whilst at the 0 of the twoglass plates-m=and meal-lying same time the frame ccan-be clearly seen throughthe' remaining part o't'the lens 7).

psdrf. four tlii n, celnente SO ris? Instead of this lens it 'is possible to a liem round m glass in Figs; 3 and 4. ,Iheilattier le Q1595. d reiad n 14 of u gi-auhd" off accordingio a spherical surface i is-aorta "eiit'e'rit"that between the single spherical zones plane-parallel parts are still left. \V'ith this lens it is thus possible to view again through the plane-parallel elementsthe object to be taken in fullsize, whilst for therestthe lens renders the col --limator frame visible.

al l iiigradusted- D simultaneously the collimator casing l,',ad-

mits-of fixin thefinderon thecamera with the aid of an extension 0; F

Iclaim: H1; i m. r15 1. In a finder for photographic cameras a collective member having the refractive zeroat least over a zone surrounding itsaxis, and a plurality of marks :lying. in the focal plane of the'saicl'collective member. 2. In a finder for photographic cameras-a lens consisting otconeentric collective zones and concentric zones having the refractive power zero interposed between the same, and aplurality of marks-lying in the-focal plane of the said lens. v I 3. In a finder according to claim 2, the zones. having the refractive power zero, being plane-parallel zones. r r 4. In a finder for photographic cameras a; collective member, a plurality of marks lying in the focal plane of this member, and means allowing of simultaneously observing on the one hand the marks throughthe said member and on the other hand direct the objectto be photographed. I I

LlEUWE EVERT WILLEM VANALBADA. 

